Does old-growth condition imply high live-tree structural complexity?

One of the most influential tenets of forest management today is that old-growth forest stands are generally more structurally complex than comparable younger stands. To test this, a chronosequence of 10 stem-mapped Douglas-firdominated mixed-conifer stands in the central western Cascades of Oregon were structurally characterized. Old-growth condition was determined using the index of old-growth (Iog); structural complexity was quantified with the structural complexity index (SCI); and spatial tree distribution patterns were evaluated with Ripley’s K function. Old-growth condition was positively related to structural complexity, but some stands with typical old-growth characteristics exhibited structures no more complex than those of transitional and mature stands. Analysis of SCI-patch types indicates that variability in structural components shifts from tree-to-tree variation to patch-to-patch variation in some old-growth stands. No consistent spatial tree distribution pattern was detected using Ripley’s K. These results suggest that managing forests to promote old-growth structural components without respect to spatial distribution, residual tree densities, tree species composition, or disturbance regime could lead to lower live-tree structural complexity.